Polyvinyl ketal acetal resin



- Patented Nov. 13, 1945 2,388,802 POLYVINYL Kr. mi. ACETAL nasnv Joseph D. Ryan,

Jr., Baltimore, Md., Ford Glass Company, tion of Ohio Toledo, Ohio, and Fred B. Shaw,

asslg'nors to Libbey-Owens- Toledo, Ohio, a corpora- No Drawing. Application April 10, 1942,

Serial No. 438,428

4 Claims. (01. 260-36) Our invention relates to polyvinyl ketal acetal resins and more particularly to a special group of these resins in which methyl ethyl ketone and butyraldehyde are the ketone and aldehyde respectively used in the manufacture thereof.

At the present time the polyvinyl acetal resins are being put to various uses such as in the manufacture of laminated safety glass, for photographic films, for coatings for fabric materials, etc. The polyvinyl acetal resins themselves are of relatively recent development and to date the butyraldehyde type of polyvinyl acetal resin has been advanced further than the other polyvinyl acetal resins, for example those made from formaldehyde and acetaldehyde. One reason for this resides in the greater ease of plasticizationof the butyraldehyd type. In fact, as a result of many experiments conducted by us, little advantage of any of the aldehydes over butyraldehyde could be found.

It is an aim of our invention to produce a new type of resin comparable with, if not superior to,

other hand, we found that not all of the aldehyde family and keton family could be combined to produce satisfactory resins but that, to the contrary, only certain of these aldehydes and ketones were suitable for use in the preparation of desirable plasticcompositions. Thus, our experimental and research work shows that some of the ketal acetal resins are hard, brittle, and inelastic, while others are water soluble and still others not compatible with plasticizers and particularly high boiling point plasticizers such as dibutyl sebacate and triethylene glycol dihexoate; or, if compatible with such plasticizers, the resulting plastic compositions lack the desired tensile strength and are subject to exudation or' sweating out of the plasticizer.

the present polyvinyl butyracetal resin and capable of various practical uses such as that of being formed into plastic compositions having remarkable properties of flexibility and resiliency coupled with great strength and toughness.

To this end, attempts were made by us to react partially hydrolyzed polyvinyl esters or polyvinyl alcohol with ketones. It is known that dimethyl ketone (acetone) or methyl ethyl ketone are widely used as solvents and are relatively cheap materials as compared, say, with the low molecular weight aldehydes. When an attempt is made to react a partially hydrolyzed polyvinyl ester or polyvinyl alcohol with low molecular weight ketones of an aliphatic nature under identically the same conditions used for preparing As pointed out above, our invention deals with a special group of polyvinyl ketal acetal resins in which methyl ethyl ketone and butyraldehyde are the ketone and aldehyde respectively used in the manufacture of the resin. We have found that under special conditions and by adherence to certain factors, it is possible to produce polyvinyl ketal acetal resins which are water insoluble and compatible with high boiling point plasthe polyvinyl acetal resins, instead of obtaining a resin in which a large proportion of the avail-- able hydroxyl groups have been replaced by the ketone, a material which is water soluble is obtained. Thi indicates'that under the ordinary circumstances, the ketones are less readily reactive and fail to replace the available hydroxyl groups.

We have, however, discovered that a resin material possessing those desirable characteristics of flexibility, resiliency, strength and toughness can be obtained under special conditions by combining not only aldehyde groups but ketone groups as well with the available hydroxyl groups of the partially hydrolyzed polyvinyl esters or polyvinyl alcohol. Such resin materials are known as polyvinyl ketal acetal resins. On the ticizers' such as dibutyl sebacate and triethylene glycol dihexoate without danger of exudation or sweating out of the plasticizer to provide plastic materials which are strong, tough and flexible.

While it is to b definitely understood, that our new resins are not limited to any particular use, one practical application thereof is in the field of laminated safety glass. Therefore, by way'of example, the resins will be particularly described herein with reference to their adaptability for and use as the plastic interlayers of laminated safety glass, it being remembered, however, that they maybe put to other uses such as in the manufacture of photographic films, .for coating fabric materials, and. for molding powders, lac quers, glass substitutes, etc.

Where the resin is to serve as the plastic interlayer in laminated safety glass, it must be stable to heat and light energy and. must have a sufficiently high boiling point and low vapor pressure that the plastic will not bubble or be otherwise unstable when subjected to the'varying temperatures encountered in normal use. Also, if laminated safety glassis made with the resin and no edge seal is used to .protect the same, the resin must show adequate resistance to hydrolysis under the conditions of normal usage. The resin must also be of such character that when properly plasticized and bonded between glass sheets, it 66 will exhibit sufficient resistance to impact at weight orpoor compatibility of the resin with plasticizers as well as high water absorption inherently results. This is more or less analogous to the findings in the polyvinyl acetal field itself where really good compatibility with plasticizers is not obtained unless one employs aldehydes having at least four carbon atoms. Methyl ethyl ketone is the most simple aliphatic ketone, next polyvinyl ketal to acetone, is a relatively cheap material, and it is to be noted contains four carbon atomsinstead of the three found in acetone. Obviously, thousands of polyvinyl ketal acetal resins can be made by reacting a partially hydrolyzed polyvinyl ester or polyvinyl alcohol with methylethyl ketone and varying the aldehyde to be employed in conjunction therewith.

I There is described in the literature a method for making mixed resins of the ketal acetal type, which comprises dissolving a polyvinyl ester in alcoholic hydrochloric acid, allowing the mixture to stand until hydrolysis of the polyvinyl ester has been carried to any desired extent, and then adding to the mixture a ketone; mixture to stand a further period of time, and

then adding an aldehyde; again allowing to stand and then finally precipitating by suitable washing operations catalyst. If this procedure is employed, depending upon reaction conditions such as concentration of catalyst, mole ratio of ketone and aldehyde to polyvinyl ester, reaction time and temperature, resins of varying composition are obtained. It should be noted at this point, however. that if there is added to the partially hydrolyzed polyvinyl ester in alcoholic HCl, a large excess in water; followed to remove the acid then allowing the of ketone, and allowed to stand indefinite periods of time, water soluble resins will be obtained. In

' other words, aldehyde apparently must be present and, being more reactive than a combined acetalization point where one obtains materials.

In the course of our investigation, we have discovered a new method for preparing polyvinyl acetal ketal resins, which method forms the basis of a separate application for patent and is therethe ketone, carries and ketalization to the water insoluble resinous I fore not a part of the present invention perse.

Based upon our experiments, however, this method is superior to that outlined in the paragraph immediately preceding and offers other advantages. Some of the pared and found satisfactory v I method and, therefore, a brief description of the method is outlined below. I j

A polyvinyl acetal resin of suitable properties is dissolved in alcohol or a mixture of alcohol and some other solvent found suitable for dissolving the resin in question. Alcoholic hydrochloric acid is then added and the solution allowed'to stand until the product of this reaction reaches the water soluble stage. This is ascertained by periodically removing diluting with water. When the water soluble resins which we pre were made by this assasoe stage has been attained, the desired ketone is then added and the mixture definite period of time at room temperature. Following this step, the'desired aldehyde may be added and the. solution again allowed to stand. The finished resin is then obtained by precipitation in water, followed by thorough washing to remove the acid catalyst. The material is then dried and ready for use.

Hereinafter we shah outline the detailed procedures used for the preparation of a number of acetal resins which we have investigated. Resins were prepared from methyl ethyl ketone, partially hydrolyzed polyvinyl acetate or polyvinyl alcohol with (1) formaldehyde, (2) acetaldehyde, and (3) butyraldehyde. Other aldehydes than those mentioned were also investigated and found to behave in a similar manner but were not explored to any great extent due to the fact that they are higher priced and might he therefore impractical at the present moment for actual production of resins. Our work shows that when formaldehyde and methyl ethyl ketone are reacted with partially hydrolyzed polyvinyl acetate or polyvinyl alcohol, resins are obtained whichdo not have good incompatible with extremely plasticizers like triethylene glycol dihexoate or dibutyl sebacate. We found that even when the vinyl alcohol content of the resin had been reduced to 20%, the resins were still incompatible with dibutyl sebacate and if reaction is conducted to a point where only 10% of vinyl alcohol is found in the finished resin, that the resins began to lack satisfactory adhesive qualities toward glass and are so soft that they are lacking-in necessary strength properties to make good safety glass interlayers. It was likewise found that methyl ethyl ketone acetaldehyde polyvinyl resins had rather higher water absorbing characteristics (even when water insoluble) than the polyvinyl butyracetal resin now used.

When experiments were conducted by reacting methyl ethyl ketone with n-butyraldehyde and partially hydrolyzed polyvinyl acetate, or polyvinyl alcohol, according to our new method described above, resins with outstandingly good characteristics could be obtained. However, in order to produce such resins, a very large amount of experimental work had to be conducted to ascertain what conditions had to be employed to samples of the mixture and give a resin of satisfactory composition. To illustrate, the reaction may be carried on under such conditions that water soluble materials are obtained or water insoluble resins may be obtained which are of poor compatibility with plasticizers. Likewise, conditions may also be chosen which will produce resins that are too soft and lacking in strength properties for safety glass interlayers.

As a result of a thorough investigation of the reaction among these three materials, besides careful analyses of the products obtained from a large number of reactions, several factors were found to be extremely important. First, and

allowed to stand over a dimethyl and diethyl phthal- Y glass manufacture.

perhaps the most important factor, is the poly- I vinyl alcohol content of the finished resin. If'

thepolyvinyl alcohol of the finished resin ranges below 50%, water insoluble resins are obtained in some cases. However, these-materials are lacking in compatibility with plasticizers and are therefore useless as bases for the manufacture of safety glass plastic interlayers. Above 50% polyvinyl alcohol content, most of the resins are water soluble and consequently not useful for safety glass manufacture.

Another factor influencing the desirability of the methyl ethyl ketone aldehyde polyvinyl resins is the ketal acetal ratio which is arrived at by determining the amount of ketone groups reacted with the hydroxyl groups of the resin by a method hereinafter: described, and likewise determining the amount of aldehyde groups reacted with the hydroxyl groups of the resin by a method also hereinafter described, and then dividing one by the other. Where the lower aldehydes were employed and reacted with' the methyl ethyl ketone and the polyvinyl alcohol or partially hydrolyzed polyvinyl ester, it was found that the ketal acetal ratio was of considerable importance. In general, the higher the ratio the better the results from the standpoint of safety glass interlayer use.

In the case of the butyraldehyde methyl ethyl ketone polyvinyl resins, this ratio was found to bealso important. The molecular weights of the butyraldehyde (72) and themethyl ethyl ketone (72) are of course identical. Attempts were made to increase the ratio of ketal to acetal, since by so doing cheapening of the resin would occur, methyl ethyl ketone being a cheaper material than butyraldehyde. pointed out, the relative reactivity of the two materials favors the aldehyde and, in general, ratios of ketal to acetal greater than from two to three were never obtained where the polyvinyl alcohol content of the resin ranged from to 28 percent. In fact, we found that when the ratio of ketal to acetal exceeded 3.25 to 1., the resin was definitely unsatisfactory for laminated safety Given below isa series of experiments detailing the method of preparation of a number of the resins prepared and investigated. In each instance, the exact reaction conditions used for preparing the resin are-outlined and an analysis of the finished resin tabulated; in those instances where analyses were not deemed necessary, for example where a resin was water soluble and of no interest, its analysis is omitted. Before giving the details of the methods used for preparing the resins of our invention, we are outlining below pertinent data regarding analytical methods,

employed in ourstudies.

Our studies show that the viscosity of the polyv'inyl esters, polyvinyl alcohol or polyvinyl acetal resins employed in the preparation of our new resins, isimportant. Where our resins are made from polyvinyl acetate directly, the viscosity is measured by dissolving the polyvinyl ester in However, as previously ester in benzene at 60 F. 'Where we employ polyvinyl acetalresins as the starting product,-

benzene and the figures given below our preparations denote the viscositymeasured in centipoises of a molar solution of the, polyvinyl theviscosity of the polyvinyl acetate from which the polyvinyl acetal resin was prepared by hydrolysis and acetalization is given and again the viscosity is expressed as that of a molar solution in benzene at 60 F. As is well understood in 'the art, the viscosity of the polyvinyl ester is the governing factor in determining the viscosity of a polyvinyl alcohol resulting from hydrolysis thereof, or a polyvinyl acetal resin made by hy- 'drolyzing the polyvinyl ester and then acetalizing to obtain thepolyvinyl acetal. We have established that resins made from polyvinyl esters having viscosities less than 7 centipoises, when measured in molar solutions of benzene at 60 F., lead to final products that are unduly brittle and,

therefore, unsatisfactory for safety glass interv layers.

' In analyzing our finished products, the vinyl alcohol content of the resins is determined by the following method:

Place 1.000 gram of the dried resin in a clean and dry citrate of magnesia-type Pyrex pressure bottle and add carefully from a pipette 25 cc. of acetic anhydride-pyridine reagent (12% by volume of acetic anhydride in dryand colorless pyridine). Cap the bottle with an ordinary bottle cap lined with silver foil. Use a pressure capper so as to prevent leaks. Place the bottle in a water bath or on a, steam plate and heat for two hours; the bottle should be shaken occasionally till the resin is completely in solution. Cool and add dropwise 2 to 3 cc. of distilled water while shaking gently and'thenlet stand at room temperature for a few minutes to allow the acetic anhydride to decompose. Wash down the cap and the mouth of, the bottle with 25 cc. of ethylene dichloride and then add from a pipette 100 cc.

of 0.5 N. alkali solution while shaking the bottle during the addition. Finish the titration with standardized 0.5 N. alkali solution using phenolphthalein (use A cc.) as an indicator; shake vigorously when reaching the end point, which is a permanent faintpink. A blank must be run.'

Cc. NaOH cc. NaOH normality for blank for sample of NaOH X04403 Weight of sample.

In determining the polyvinyl acetate content of our finished resins, the method outlined below is employed: 1

Place 1.000 gram of the dried resinin a clean and dry citrate of magnesia-type Pyrex pressure Xl00= vinyl alcohol bottle and add from a pipette 50 cc. of methanolbutanol solution (5 methanol to 1 butanol) in.

such a way as to wash down the sides of the bottle. From a burette add exactly 10 cc; of

.15 N. NaOH. Cap the .bottle with an ordinary pressure bottle cap lined with silver foil. Use a capper so as to prevent leaks. Heat the mixture either in a water bath won a steam plate for two hours. Without cooling, dilute with 50 cc. of butyl alcohol and add from a burette 10 cc. of .2 N. H2804 solution; recap and heat for an addlitional 30 to 45 minutes. Cool and titrate with .15-N. NaOH solution, using bromthymol blue as A blank must be run.

X for blank oiNaOH Xmo=% vinyl acetate Weight of sample for sample bur studies show that resins having a polyvinyl acetate content of more than 5% are less duction of AgNOs.

= to the shortened mainthe phosphoric acid and water during the digessatisfactory for safety glass inter-layers than those having a lower polyvinyl acetate content. In order to arrive at the polyvinyl acetal content oi. the resins. we adopted the following pro-- cedure:

Dnrlamarron or Ponyvmn. Ace-ran m vmn. Acrru. Km Rlsnrs Principle 7 Digestion-in phosphoric acid followed by distillation and determination of aldehyde byre- Pou- Apparatus v 'A'Claisen flask of 500 cc. capacity, with th main neck shortened so as to eliminate dead air space, is connected with an extra long water condenser fitted (tightly) with an adapter. The

adapter is long enough to reach the bottom oi the distillate flask, preferably a 1 liter glass stoppered bottle. Rubber stoppers are used'at all connections. A dropping funnel is connected neck and is usedto' add A .25-.50 gram sample of the dried resin is weighed into the Claisen flask and 100 cc. of

' phosphoric acid (40-45% added. The apparatus is connected and 50 cc. of distilled water placed in the receiver so that the end of the adapter is :below the water. The receiver is immersed in anice bath and all precautions are used to prevent th escape of aldehyde. Heat is applied slowly so that when the resin dissolves, the solution will be clear and dark amber in color.

Some distillation will take place while resin is dissolving andwater should be added through Cc. tbiosuliata for blank-cc. thiosuliate for sampleXnormallty of thiosulieteXmol. wt. of polyvinyl ketalXlOO lOOOXsaml lB wt. 6

the dropping funnel to compensate for this. After resin dissolves, the solution is distilled at a rate aaeaeos followed by determination of, ketone by iodoform this method is applicable which form iodoform. Al-

method. Obviously, only to those ketones dehydes which form iodotorm interfere.

. Apparatus The same as that described under the determination of polyvinyl acetal in P yviny Metal ketal resins. 4

' Solutions Phosphoric acid-404595. NaOH solution-108 grams per 300 cc. 1/10 N. iodine in KI solution. Concentrated HCl. I

1/10 N. sodium thiosulfate.

Digestion A .25 gram sample of the dried resin is weighed into the Claisen flask and 100 cc. of phosphoric acid (40-45%). added. The apparatus is connected and 50 cc. of distilled water placed in the receiver so that the end of the adapter is below the water. The receiver is immersed in an ice bath and all precautions are used to prevent the escape of ketone. Heat is applied slowly so that when the resin dissolves the solution will be clear and dark amber in color. Some distillation will take place while resin is dissolving and water should be added through the dropping funnel to compensate for this. After resin dissolves, the solution is distilled at a rate that will give a 350 cc. distillate in approximately one hour; water being added through the dropping funnel at the same rate.

Determination The distillate is weighed and cone. NaOH is added (11 cc. for every 100 cc. of distillatehiollowed by cc. of 1/10 N.'iodine solution. The mixture is allowed to stand 15 minutes. At this point the iodoiorm is usually precipitated. The solution is then acidified with conc. HCl (cooling in ice bath) until all the iodine is liberated. The. liberated iodine is then titrated with standard 1/10 N. sodium thiosultate.

Calculations %pclyvinyl kstal Dnrsnmminon or Sun or new. arm Acnrai. Conthat will give a 500 cc. distillate in approximately 1 hour; water being added through the dropping funnel at the same rate.

Determination tent of both blank and sample is determined by any of the standard methods. Calculations ramm Ponrvnwr. Acursr. KETAL Rssms Principle Sum 01' ketal and acetal contents obtained by digestion in phosphoric acid, followed by distillation anddetermination by means of NaHSOs.

Apparatus The same as that described under the determination of polyvinyl acetal in polyvinyl acetal ketal resins. Solutions Phosphoric acid-404595 N .2 grams per 100 cc. H20 1/10 N. iodine solution l/20 N. sodium thiosuliate solution l% starch solution Wt. of AgCl in blank-wt. oi AgOlin samplleXlOOXmol. wt. of pol -5 metal pol I 1mm Sample wt.X286

DETERMINATION orPoiiitvmn. KITAL nv Ponrvr'nn Kern. Acs'ru. Rrsms Principle Digestion'in phosphoric acid and. distillation Diflestion Sample weight should be .6 to 1 gram. 'riie digestion and distillation are carried out as explained in'the determination of polyvinyl ketal in pohrvinyl ketal acetal resins. 500 cc. of dissolved in 1000 cc. of ethylene dichloride.

tillate are collected. Both ketal alone or ketalacetal together may be determined with this-one distillation.

. Titration For combined acetal and ketal, pipette a 50 cc. portion of the distillate into a 100 cc. volume flask. Add, With pipette, cc. ofbisulfite solution, and then dilute to mark with distilled water. Let stand one hour. A 50 cc. portion is then pipetted into a flask containing 50 cc. of 1/ 10 N. iodine solution and 5 cc. of 50% acetic acid. The

ekcess iodine-is titrated immediately with 1/20 N.

sodium thiosulfate to astarch end point. A

blank, using distilled water in place of distillate,

must be run simultaneously.

Calculations A. (-c. thiosulfate-00. thiosulfateXnormality volume oiX2 for sample for blank thiosulfate distillate IOOOXsample wt. 50X2 EXAMPLE No. 2.POLYVINYL AcErAL KErAL RESIN rnom FORMALDEHYDE nn METHYL ETHYL KETONE Preparation 135 grams of polyvinyl acetate resin* which was made by reacting a partially hydrolyzed polyvinyl acetate of viscosity centipoises (molar benzene solution at 60 F.) with formaldehyde was dissolved in 1000 cc. of ethylene dichloride. 360 cc. of methyl ethyl ketone was added followed by immediate addition of 100 cc. of methanolic hydrochloric acid (4.6 normal). The mixture was then allowed to stand for 15 hours. At the end of this period of time, the ethylene dichloride was removed by distillation and the resulting residue diluted with water and the precipitated product I filtered off, washed free of acid-catalyst and then Total moles of carbonyl groups (or equivalents) l3. (Equivalents of polyvinyl ketal can be determined on 100 cc. portions .of the 500 cc. distillate. The procedure is the same as that described under the polyvinyl kctal analysis.)

(c. thiosulfate-cc. thiosulfateXnormality Xvolume of for blank for sample thiosulfate distillate lOOOXsample wt. 100 6 Equivalents corresponding to polyvinyl ketal Therefore: AB=equivalents corresponding to polyvinyl acetal. Since the bisulfite reaction is only 90% complete, the

percent bf polyvinyl ncetal= T XmoL wt. of polyvinyl acetal The percent of polyvinyl ketal=B moL wt. of polyvinyl ketal.

EXAMPLE No. 1.-POLYVINYL AcErAL KE'rAL RESIN FROM FoRMA'LnEnYnE AND METHYL ETHYL KE'roNE Preparation Analysis Per cent Polyvinyl alcohol 18.8 Polyvinyl acetate 7.5 Properties This resin when plasticized with 50 parts of dimethyl phthalate per 100 parts of resin gave a transparent sheetwhich'was inelastic and hard. With 50 parts of dimethyl sebacate, dibutyl phthalate and dibutyl sebacate', the resin was incompatible. In the case of the dimethyl sebacate,; a plastic sheet was obtainedbut the plasticizer exuded rapidly.

The resin was unsatisfactory for safety glass.

Analysis .Per cent Polyvinyl. formal 82 Polyvinyl alcohol 8.7 Polyvinyl acetate 9.2

dried.

Analysis Per cent- Polyvinyl alcohol 13.8 Polyvinyl acetate 7.35 Properties While this resin material when plasticized with 50 parts of dimethyl phthalate to parts of resin gave a transparent sheeting, the material was found to be inelastic. Plasticized with 50 parts of dimethyl sebacate, a sheet was obtained which sweated out badly. The resin was found to be incompatible with dibutyl phthalate and dibutyl sebacate.

This resin material did not yielda satisfactory safety glass interlayer.

Analysis Per cent Polyvinyl formal 82 Polyvinyl alcohol 8.7 Polyvinyl acetate 9.2

EXAMPLE No. 3.'--PoLYvINYL AcE'rAL KETAL RESIN FROM FORMALDEHYDE m) METHYL ETHYL KETONE Preparation grams of polyvinyl acetal resin" which was made by reacting a partially hydrolyzed polyvinyl acetate of viscosity 15 centipoises (molar benzene solution at 60 F.) with formaldehyde was dissolved in 1000 cc. of ethylene dichloride. 360 cc.

of methyl ethyl ketone was added followed by immediate addition of 100 cc. of methanolic hydrochloric acid (4.6 normal). The mixture was then allowed to stand for 24 hours. At the end of this period of time, the ethylene dichloride was removed'by, distillation and the resulting residue diluted with water and the precipitated product -filtered oil, washed free of acid catalyst and then dried.

"Analysis Per cent Polyvinyl alcohol 24.0 Polyvinyl ac 6.05

Properties When plasticized with 50 parts of dimethyl phthalate to 100 parts of resin, a hard'horny sheet was obtained. The resin was incompatible with dibutyl phthalate, dimethyl sebacate and dibutyl sebacat This resin did not yield a satisfactory safety glass interlayer.

Analysis Percent Polyvinyl formal -L 82 Polyvinyl alcohol 8.7

Polyvinyl 'acetate 9.2

M No. 4.Por.xvnnn. Acrrn. Kz'ru. Rnsm no! ACITALDIHYDI Arm Mum Erma. Karon Preparation 135 grams of polyvinyl acetal resin which was made by reacting a partially hydrolyzed polyvinyl acetate with acetaldehyde (viscosity of the polyvinyl acetate being'15 centipoises in molar ben- Analysis No analysis was made because the product was water soluble.

Properties Obviously, the water solubility of the resin made it unsatisfactory for safety glass and experimentation shows that such water soluble resins are incompatible with high boiling point plasticizers such as dibutyl sebacate.

, type described, used for the preparation of theff resin in Examples 4 and 5. was dissolved in 500;"; cc. of methanol. To this solution was added 180 cc. of methyl ethyl ketone and 200 cc. of methanolic E01 (2.75 normal) The mixture was al-- lowed to stand for 48 hours, and then poured into water. The material precipitated but readily redissolved in the water. Precipitated in other-solvents it was found to. be water soluble.

Analysis No' analysis made due to high water solubility.

Properties Resin unsatisfactory 'for safety. glass inter- I layers.

EXAMPLE No. 7.PoLYvmYL ACETAL KETAL Rasm FROM AcarALnanYnn AND METHYL ETHYL Karons Preparation I soluble. This point was ascertained by periodically removing samples of the product and testing for water solubility. The time necessary to reach this stage was approximately 3 hours. At this juncture 300 cc. of methyl ethyl ketone was added Analysis Percent Polyvinyl alcohol 9.49 Polyvinyl acetal 57.8 Polyvinyl acetate 29.2

Exmra No. 5.--POLYVINYL ACETAL KE'lAL Rssm non Acerunmrnn AND Marina. Erma. Karena Preparation 135 grams of polyvinyl aoetal resin which was made by reacting a partially hydrolyzedpolyvinyl acetate with acetaldehyde (viscosity of the polyvinyl acetate being 15 centipoises in molar benzene solution at 60 F.) was dissolved in 1000 cc. of methanol. 360 cc. of methyl ethyl ketone was added. and immediately was also added 400 cc. of methanolic E01 (2.75 normal). The mixture was allowed to stand for 6 hours, then poured into water, and it was found that hot water was necessary to precipitate the resin. After washing with hot water to remove acid catalyst, the material was air dried.

Analusis 7 Per cent Polyvinyl alcohol 34.5 Polyvinyl acetate 8.6

Due to the fact that the resin had such high water solubility, a complete analysis was deemed unnecessary.

Properties This resin was found to be somewhat soluble in cold water, less so in hot water. It formed a thin gel with methanol. Its compatability with high boiling point plasticizers was found to be unsatisfactory, making it unsuitable for safety .glass use. 7 Analysis Per cent Polyvinyl alcohol 9.49 Polyvinyl acetala 57.8 Polyvinyl acetate 29.2

Exmm' No. 6.-Por.rvmr. Acruu. Kerm- Rzsm no! Acn'rllmmrnn um Mnrmrr. Erma. Karon:

Preparation 67 grams of a polyvinyl acetal resin 01' the ome and the mixture allowed to stand for 3 hours.

Then 250 cc. of acetaldehyde was added and again the mixture allowed to stand for 16 hours. The product ofthis reaction at this point was recovered by pouring the solution into water with vigorous stirring; it was then washed free of acid catalyst with water and dried.

A complete analysis was not made on this resin since it was found unsatisfactory for safety glass.

Properties When plasticized in the usual way on heated rolls using parts of the resin to 40 parts of dibutyl 'sebacate, it was found that the dibutyl sebacate was not compatible with the resin; that is to say, the plastic sheeting underwent exudation. With dimethyl sebacate, a stiff inelastic plastic sheet was formed by compounding 100 parts of the resin with 40 parts of dimethyl sebacate unheated rolls followed by calendering. Plastic made using 100 parts of the resin to 40 parts of dimethyl phthalatewas found to be hard and horny while plastics made with a similar quantity of dibutyl phthalate underwent exudation. The resin was 'found to be slightlywater soluble, and unsatisfactory for safety glass interlayers due to its'brittleness and non-compatibility.

Exam No. 8.-PoLYvmYr. Acsru. Ks-rsr. 'Rrsm non Acnrarnema AND Marm Erma. Karena Preparation grams of polyvinyl acetal resin of the same type used for the preparation of the resin in Examples 4, 5, 6 and 7 was dissolved in 1000 cc. of methanol. 400 cc. of methanolic HCl (2.5 nor- 1 mal) was added and the solutionallowed to stand water. The period of time required to reach this stage was about 3 hours. 360 cc. of methyl ethyl ketone was added and the mixture then allowed to stand for 16 hours. 200 cc. of acetaldehyde was then added and the solution allowed to stand an additional hour. The resinous product was recovered by pouring the mixture into water with vigorous stirring followed by filtration and washing to remove acid catalyst; it was then air dried.

Analysis Per cent Polyvinyl alcohol 20.9 Polyvinyl acetate .8 Properties Plastic sheetings were made by compounding 100'parts of this resin with 40 parts-of dibu-tyl sebacate, dimethyl sebacate, dimethyl phthalate and dibutyl phthalate respectively. In the case of the plastic sheeting made with dibutyl sebadate, it was found to be hard and inelastic .and as well underwentexudation. The sheeting made with dimethyl sebacate was stiff, brittle and inelastic. The sheeting made with dimethyl phthalate was also stiff and inelastic. In the case of the sheeting made with dibutyl phthalate,

it was likewise brittle and inelastic. None of these four types of sheeting were satisfactory for laminated safety glass interlayers, being too brittle especially at low temperatures. It is interesting to note that although the combined acetal ketal content of the resin was approximately 80%, the resultant resin is lacking in compatibility with suitable plasticizers and unsatisfactory for safety glass.

EXAMPLE NO. 9.POLYVINYL ACETAL KETAL RESIN MADE FROM BUTYRALDEHYDE AND METHYL ETHYL.

KETONE Preparation 688 grams of polyvinyl acetate (viscosity 4 centipoises) was dissolved in 3200 cc. of methanol.

drying. Analysis Polyvinyl alcohol per cent 35.9- Polyvinyl acetate do .9 Polyvinyl ketal do 49.7 Polyvinyl acetal do 13.48 Ratio of ketal to acetal v 3.6

Properties 800 cc. of methanolic HCl (4.6 normal) was then added and the mixture allowed to stand until the product of this reaction was water soluble (2 hours). then added and the solution allowed to stand for 1 hour, when 240 cc. oi n-butyraldehyde was added. This mixture was then allowed to stand for 13 hours. The resinous product was recovered by pouring the mixture into water, filtering, washing free of acid catalyst with water, and drying.

Analysis Polyvinylalcohol per cent 36.9 Polyvinyl ketal do.. 51.5 Polyvinyl acetal do 11.3 Polyvinyl acetate do ,3 Ratio of ketal to acetal 4.56

Properties 7 When this resin was inade into plastic byplasticizing 100 parts with 40 parts of dibutyl sebacate, in the usual manner, it was found that the sheeting underwent exudation or sweating out of plasticizer. It was observed that the sheeting was inelastic and rather brittle. Similarly resultswere obtained when attempts were made to make plastic sheeting using dimethyl phthalate,

dibutyl phthalate and dimethyl sebacate. While 1n the case of dimethyl sebacate and dimethyl phthalate, sweating out was not observed, the sheeting was inelastic and brittle. This resin, our tests show, would be unsatisfactory for a laminated safety glass interlayer and, as an ex- 400 cc. of methyl ethyl ketone was mixture allowed to stand for 15 hours.

amination of the analysis above given shows, in this case we have a polyvinyl alcohol content of 36.9%. the polyvinyl alcohol content establishes that when the polyvinyl alcohol content exceeds 25%, the resins are unsatisfactory for safety glass interlayers.

EXAMPLE No. 10.Por.YvmY L ACETAL KETAL Rasm Mans mom BUTYRALDEHYDEAND METHYL Ernxr. Karon:

' Preparation 172 grams of polyvinyl acetate (viscosity 45 centipoises) was dissolved in 800 cc. of methanol. 200 cc. of methanolic HCl (4.6 normal) then added. The mixture was then allowed to stand until the product of this reaction was watersoluble (approximately 2 hours). At this point 100 cc. of methyl ethyl ketone was added and the mixture was allowed to stand for 2 hours. Then 60cc. of n-butyraldehyde was added and the mixture allowed to stand for 15 hours. At this point additional methanol was added and the resin precipitated in water, followed by washing and This resin was found to be compatible with dimethyl phthalate but gave a rather inelastic sheeting. With dibutyl phthalate, a stiff inelastic sheet was obtained, and with dimethyl sebacate and dibutyl sebacate. the resin was found to be on the edge of compatibility, yielding inelastic products. I

The material is found after extensive testing to be unsatisfactory for safety glass interlayers.

EXAMPLE No. 11.-POLYVINYL Acarar. KE'I'AL MADE FROM BUTYRALDEHYDE AND METHYL ETHYL Ks- TONE Preparation and drying. Analysis- Polyvinyl alcohol ..per cent 8.2 Polyvinyl acetate do 3.9 Polyvinyl ketal do 45.44 Polyvinyl acetal do 42.48 Ratio of ketal to acetal 1.0'l

Properties This resinous material was found to yield soft elastic sheetings with dimethyl phthalate, dimethyl sebacate; dibutyl phthalate and dibutyl sebacate. However, the sheeting was soft and lacking in tensile strength. At elevated tempera- A series of resins made by varying tures, laminated glass made withthis material had inadequate resistance to impact.

Ebumru No. 12.Por.rvnwr. Amer. KETAL Rasm Mm: raou Bmnarnmnz m Mim-ryr. Err-1Y1.

Ksrom:

Preparation 600 grams of polyvinyl acetate of viscosity 45 centipoises was dissolved in 3000 cc. of methyl ethyl ketone and 3000 cc. of methanol. Then 1200 cc. of methanolic I-ICl (3.0 normal) was added and the mixture stirred for 18 hours. 1200 cc. of butyraldehyde was added at this juncture and stirring continued for 6 hours. The resin was recovered by precipitation in water in the usual manner.

Analysis Polyvinyl alcohoL; per cent 7.3 Polyvinyl keta do 40.4 Polyvinyl acetal do 40.! Polyvinyl acetate do 11.6 Ratio of ketal to acetal. 1.00

Properties sebacate respectively to 100 parts of the resin and calendered to produce .015 inch. stock, it was laminated" between glass withoutadhesive in the standard manner. Break tests using a freely falling half-pound steel ball conducted on 12 x 12 inch laminations made fromthese two plastic sheetings at 70 and 120 F. gave the following results: At 0 the 33 parts stock withstood the impact of the ball 16 feet, while at 70 about 40 feet, and at 120 the laminations failed to withstand thei'mpact of the ball falling feet. The 40 parts stock at 0 withstood the impact of the a,see,eoa

cc. of methanolic HCl (3.0 normal) was addedv to the solution and the mixture stirred for 1% hours. The mixture was then allowed to stand for 97 hours and became a toughgel. At the end'of this time 1350 cc. of butyraldehyde and 2000 cc. of methyl ethyl ketone were added and stirring continued for 48 hours. brought about complete solubility of the'gel and at the end of this 48 hour period, the resinous product was recovered by precipitating in water. The product was recovered by filtration, washed with water to remove acid catalyst and was then dried.

Analysis Polyvinyl alcohol per cent 12.0 Polyvinyl ketal do 54.5 Polyvinyl acetal do.. 32.8 l olyvinyl acetate do 0.7 Ratio of ketal to acetal 1.66

Properties This resin was found to possess excellent compatibility properties with dimethyl phthalate,

dimethyl sebacate, dibutyl phthalate and dibutyl sebacate. Sheeting was made on hot malaxating rolls, followed by calender ing, and when sheets of the plastic .015 inch in thickness, made by compounding 100 parts of the resin with 33 parts of dibutyl sebacate, were laminated between plates of glass without adhesive by stand- "ard laminating procedures, an excellentproduct was obtained. 12 x 12 inch samples of laminated safety glass made from this sheeting and impacted at 0", 70 and 120. F. with a halfpound; freely falling, steel ball, gave the followhalf-pound ball falling 20 feet, while at 70 the laminations withstood-the impact of the ball about 30 feet, and at 120 the laminations failed to withstand the-impact of the ball 18 feet. It

was observed that the laminated glass made from both these stocks was satisfactorily stable to ultra-violet light and weathering unsealed.

It will be observed that in this case the polyvinyl alcohol content of the resin was 7.3% and the polyvinyl acetate content 11.6%- The resultant resin, it is to be noted, is somewhat too soft and lacking in strength properties for laminated safety glass, especially at high temperatures. Investigation of a number of resins shows that when the polyvinyl acetate content greatly falls below 10%, such resins have unsatisfactory :grength, especially at elevated temperatures, say 0 F.

centipoises in molar benzene solution at 80 F.)

was dissolved in 3000 cc. of methanol and 3000 cc. of methyl ethyl ketone was then added 1200 ing results: The laminations at 0 withstood the impact of the ball falling through a distance of 16 to 18 feet, 'and at 70 the laminations withstood the impact of the ball over 40 feet, while at 120 F. the laminations withstood the impact of the ball falling through a distance of 16 to 18 feet. When 100 parts of the resin was plasticized with 40 parts of dibutyl sebacate, the resultant sheeting laminated between glass withstood the impact of the half-pound steel ball falling on a 12 x 12 inch lamination more than 20 feet at 0, over 40 feet at 70, and about 18 feet at 120 F.

The laminated glass made from this resin was found to possess excellent light stability as well as excellent resistance to weathering when 'ex- Exams: No. 14.POLYVINYL Acorn. Kz'mr. Rrsm exceeds 5.0% and the polyvinyl alcohol content Mann mom Burmrnnms AND'METHYL Erin-r. Knom:

Preparation 1032 grams a polyvinyl acetate of viscosity 45 centipoises was dissolved in'4980 cc. of methanol. Then 600 cc. of methanolic HCl (7.29 normal) added and the solution allowed to stand until the product became water soluble. 366 cc. of methyl ethyl ketone was then added and at the end of 1 hour, an additional 366 cc. of methyl ethyl ketone added. The solution was allowed to stand for 3 hours. .At this point 600 cc. of nbutyraldehyde was added and the resulting mixture allowed to stand for 16 hours; The resinous product was recovered by pouring the solution with water to remove the acid catalyst and dried.

This treatment falling, steel ball a distance of-18 feet. At '10" F. the 12 x 12 inch laminations withstood the im- Analysis Polyvinyl alcohol per cent 14.4 Polyvinyl ketal do 46.08 Polyvinyl acetal do 37.12 Polyvinyl acetate do 2.4 Ratio of ketal to acetal- 1.24

' Properties When 100 parts of this resin was compounded with 37 parts of dibutyl sebacate, an excellent plastic sheeting for safety glass was obtained. Laminated glass, 12 x 12 inch in size, made with this plastic sheeting without adhesive in .015 inch thicknesses, successfully withstood the impact of a half-pound steel ball falling freely; 40 to 45 feet at 70 F., 18 feet at F., and 16 feet at 120 F.

This resin was found to be compatible with other plasticizers such as dimethyl phthalate,

dimethyl sebacate, dibutyl phthalat'e, dibutyl sebacate, BGH, etc. Like resin in Example 13,

' this resin was found to bewater insoluble and possessed a low water absorptive power when exposed to very high relative humidities. The

- laminated safety glass described above made with this resin was found to possess excellent light and weathering resistance unsealed.

ExAMPLa No. 15.POLYVINYL ACETAL KE'I'AL RESIN Minna mom BUTYRALDEHYDE AND METHYL ETHYL Karon:

Preparation 1032 grams of polyvinyl acetate (viscosity 45 centipoises) was dissolved in 4980 cc. of methanol. 600 cc. of methanolic E01 (7.92 normal) was then added and the solution allowed to stand until the product of this reaction was water soluble. This,

of course, was as usual ascertained. by periodic sampling of the mixture and testing for water solubility. The time required in this instance to reach this stage was 2 hours. ethyl ketone was then added and the solution allowed to -stand 11 hour. At this time 366 cc.

additional methyl ethyl ketone was added and the mixture allowed to stand 3 hours; then 600 00.01 n-butyraldehyde was added and the mix-.- ture allowed to stand for 16 hours. The resinous product was recovered by precipitation or the water, filtration, washing with water, and

then drym g.

Analysis Polyvinyl alcohol per cent 22.2 Polyvinyl ketal i do 42.9 Polyvinyl acetal do-- 34.1 Polyvinyl 'acetate do .87 Ratio of .ketal to acetal -..1.26

I Properties and transparent and, when laminated betweenclean plates of glass without adhesive, in any 360 cc. of methyl pact of a half-pound, freely falling, steel ball 45 v to 50 feet, while at 120 F. the laminations withstood the impact of the half-pound ball 24 feet.

Accelerated weather tests, light tests, and exposure tests on these laminations show them to possess excellent stability, proving that they can be used in commerce, unsealed.

EXAMPLE No. 16.---POLYVINYL ACETAL Karat. REsm Mans mom BUrYnALm-mxns AND Marma- E'rm KETONE Preparation 792 grams ofv polyvinyl acetate (viscosity 45 centipoises) was dissolved in 4200 cc. of methanol.

792 cc. of methanolic HCl (2.65 normal) was then added and the solution allowed to stand until the product became water soluble (3 hours). 792

cc. oi. methyl ethyl ketone was then added and the solution stirred 30 minutes. 1800 cc. of methanolic HCl (2.65 normal) and 1200 cc. of methyl ethyl ketone added. On standing 18 hours, half of this mixture was treated with 600 cc. of n-butyraldehyde and stirred until the solution became complete. The resin was recoveredby precipitation in water, washing and air drying.

Analysis Polyvinyl alcohol.. per cent-.. 18.5 Polyvinyl ketal do 51.9 Polyvinyl acetal do 24.8- Polyvinyl acetate do 4.8 Ratio of ketal to acetal 2.09

Properties This resin, like the resinin Example 15, was

found to be an excellent base for making safety glass plastic interlayers. It possessed excellent compatibility with dibutyl sebacate and dibutyl phthalate. Plastic plasticized with 40 parts oi dibutyl sebacate had low water absorptive properties. 12 x 12 inch laminations made by interposing .015 inch layers of plastic, made by compounding 100 parts of this resin with 40 parts of dibutyl sebacate, between clean sheets of glass,

without adhesive, were tested for resistance to impact at 0,-70 and 120 F. using the halfpound, freely falling, steel ball. At 0 the laminations withstood the impact of the half-pound steelball 22 feet. At F. about 40 feet, and at 120 F. 18 feet.

Examrm No. 17.--Por.YvmYr. Acs'rA L'KsrAr. Rssm' Mans FROM BUTYRALDEHYDE m Mama Eran KETONE Preparation 172 grams of polyvinyl acetate (viscosity 45 centipoises) was dissolved in 800 cc. of methanol.

200 cc. of methanolic H01 (4.6 normal) then added. The mixture was then allowed to stand until the product of this reaction was water soluble (approximately 2 hours). At this point 100 cc.-of methyl ethyl ketone was added and the mixture was allowed to stand for 1 hour. Then 60 cc. of n-butyraldehyde was added and the mixture allowed to stand for 15 hours. At this point,

' additional methanol was added and 'the resin standard-manner, the 12 x 12 inch laminations I impacted at 0 F. withstood the halt-pound, freely precipitated in water followed by washing and ying.

Analysis V Polyvinyl alcohol per cent ..17.6 Polyvinyl aceta do 1.3 Polyvinyl ketal do 44.02 Polyvinyl aceta 7.1

Ratio of ketal to acetal. 1.18

.patible with dimethyl phthalate, dimethyl sebacate, dibutyl phthalate, and dibutyl sebacate, giving tough elastic transparent sheets which, when laminated between glass, gave a very satisfactory safety glass product. Impact tests showed the laminations to have good cold resistance and satisfactory resistance to impact throughout the range of to 120 F. Laminated safety glass made with this material was tested for light and heat stability and found to be satisfactory. Due

to the low water absorption of the resin, the

laminated safety glass made using this resin as an interlayer did not require edge sealing.

It will be noted that those resins shown above (Examples 13 to 17) as being suitable for safety glass use were all made from butyraldehyde and methyl ethyl ketone, while the resins made from formaldehyde. and methyl ethyl ketone and acetaldehyde and methyl ethyl ketone were found unsatisfactory for safety glass manufacture. Furthermore, it should be emphasized that not all of the resins made from butyraldehyde and methyl ethyl ketone (Examples 9 to 12) were satisfactory for use as plastic interlayers in laminated safety glass. However, we discovered that butyraldehyde and methyl ethyl ketone could be obtained to produce a resin eminently suited for use in the manufacture of laminated safety glass providing certain factors were adhered to'such as the vinyl alcohol content of the resin, the vinyl acetate content of the resin, the viscosity of the polyvinyl esters or partially or wholly hydrolyzed polyvinyl esters, or polyvinyl acetal resins employed as the starting product in the preparation of our new resins, and the ratio of the ketal acetal content. In other-words, our work shows that the vinyl alcohol content of the resin (calculated as polyvinyl alcohol) must fall between 10 and 28 percent; the vinyl acetate content of the resin (calculated as polyvinyl acetate) should be less than 5 percent; the polyvinyl acetate used as a starting product in the preparation of our new resins, before partial or entire hydrolysis, should have a minimum viscosity of less than 7 centipoises in molar benzene solution at 60 F., and the ratio of ketal to acetal should preferably be not less than .5 to 1 and not exceed 3.25 to 1. Resins of the above character, having these special properties, can be suitably combined with high boiling point plasticizers and satisfactorily used as interlayers in laminated safety glass.

It will be noted in describing our resins that under the heading "Properties, comments on the Plasticization of the various resins are made. Having found certain resins as indicated above (Examples 13 to 17) which were suitable for safety glass, a comprehensive study was made of the plasticization of these materials. Some plasticizers like dimethyl phthalate and diethyl phthalate, although compatible, were found to yield plastics which were too soft for safety glass interlayers or were too brittle at low temperatures when used as a safety glass interlayer. In the cases of dimethyl and diethyl phthalate, for example, when the plasticizer content was increased to a point where satisfactory impact resistance of the laminations was obtained at low temperatures, the plastic sheeting was very soft and taclqr at normal temperatures and could not be handled satisfactorily in a manufacturing operation. It was likewise observed that on standing, the plastic materials made with mate- 'glass, however, it is preferred that our new type of resin be plasticized with materials such as dibutyl sebacate, triethylene glycol dihexoate.

-esters made from triethylene glycol by reaction with'the fatty acids of cocoanut oil, and as well esters made by reacting primary monohydric alcohols with the acids obtained when cresylic acid is hydrogenated and then oxidized to yield mixtures of substituted adipic acids.

After preparing the. resins in the above described manner, those indicated as being suitable for safety-glass plastic manufacture (Examples 13 to 17) were plasticized by adding 100 parts of resin to' from 35 to 60 parts of plasticizer and worked into transparent sheeting by any of the so that the plasticizer wets the particles of the resin. This mass was then transferred to a malaxating roll and kneaded at elevated temperatures (250 to 300 degrees F.) until the plasticizer had peptized or dissolved the resin. The mass was then made into sheet form by calendering on rolls. Instead of the calendering operation, the mass in one instance was cut into small slabs, placed in a steel mold, and pressed into cake form at elevated temperatures.

thickness .015"). In another method, the resin and plasticizer were dissolved in denatured alcohol, using only sufficient alcohol to give a very viscous mass, and then extruded from a slot into sheet form, dried free of volatile solvents, and was ready for lamination. -In the actual manufacture of the laminate glass, the resin sheets were inserted between twoclean plates of glass, no adhesive being employed,

' and the sandwich so formed pressed in a platen press and subjected to a pressure of 50 pounds per square inch at 250 degrees F. for three minutes. Leaving the platen press, the laminations were introduced into an autoclave containing oil, and subjected to true hydraulic pressure at a temperature of 2'75 degrees F. for a period of seven minutes under a pressure of 225 pounds per square inch. Instead of resorting to the platen press, in some instances the sandwiches, for preliminary closure before autoclaving, were heated in an oven at a temperature of 250-degrees F. and then run through nippin rolls. The finished laminated glass was found to possess excellent optical characteristics, good stability to heat as measured by immersion in boiling water for a period of ten hours; found to possess excellent resistance to ultra-violet light as measured by exposure to the Uviarc for a period of 1000 hours; and found to possess excellent weathering characteristics by exposure to an accelerated weather test. One accelerated weather test cycle consisted of placing the lamination in a chest maintained at degrees F. saturated with water vapor, followed by a 24 hour heating in dry air at degrees F., followed by a 24 hour exposure in a refrigerator at zero degrees F.

The block so formed was then skived into sheets of the desired 4 assaeos ins 45 feet; while the laminations maintained at 120 degrees F. withstood the impact of a halfpound steel ball falling 24 feet. In the above instance, the plasticizer content was 40 parts of dibutyl sebacaw per 100 parts resin. andour experimental work shows that as the plasticizer content is decreased, increasingly greater resistance to impact is obtained at 70 and 120 degrees F., while if increased above 40 parts. greatly increased resistance to impact is obtained at zero degrees ,with an accompanying decrease in strength at the elevated temperatures of 70 and 120 degrees F.

Although the improved resins herein provided have been described with particular reference to their use as the plastic interlayers of laminated safety glass, it will be understood, s pointed out above, that they are not restricted to such use but, on the contrary. may be put to various other uses for which they are adaptable. Cross reference is herein made to our copending application filed March 21, 1942, Serial No. 435,714, and more particularly claiming the use of our improved resins in the manufacture of lamina safety glass.

We claim:

1. A synthetic resin plastic which comprises a polyvinyl ketal acetal resin formed by the reaction of a hydrolyzed polyvinyl acetate (the vis cosity of the polyvinyl acetate used as a starting product having a minimum viscosity of 'l centinoises in molar benzenesolution at 60-degrees F.) with methyl ethyl ketone and butyraldehyde and characterized by the fact that the vinyl alcohol content or the resin (calculated as polyvinyl alcohol) ranges between .10 and 28 percent, the vinyl acetate content of the resin- (calculated as polyvinyl acetate) is less than percent and the ratio or the ketal to acetal content is not less than.5to1anddoesnotexceed3.25tol.and

content of the resin (calculated as polyvinyl ala plasticizer therefor comprising an ester of straight chain dicarboxylic acid containing more than four methylene groups.

2. A synthetic resin plastic which comprises a polyvinyl ketal acetal resin formed by the reaction of a hydrolyzed polyvinyl acetate (the viscosity of the polyvinyl acetate used as a starting product having a minimum viscosity of 7 centi noises in molar benzene solution at 60 degrees F.) with methyl ethyl ketone and butyraldehyde and characterized by the fact that the vinyl alcohol content of the resin (calculated as polyvinyl alcohol) ranges between 10 and 28 percent, the vinyl acetate content of the' resin (calculated as' polyvinyl acetate) is less than 5 percent and the ratio'of the ketal to acetal content is not less than .5 to 1 and does not-eXceedBfaB to 1, and

a plasticizer therefor comprising dibutyl seba-- cate.

3. A synthetic resin plastic which comprises a polyvinyl ketal acetal resin formed by. the reaction of a hydrolyzed polyvinyl acetate (the V18? cosity oi the polyvinyl acetate used as a starting product having a minimum viscosity of '1 centipoises in molar benzene solution at 60 degrees F.) with methyl ethylketone and butyraldehyde and characterized by the fact that the vinyl alcohol cohol) ranges between 10 and28 percent, the vinyl acetate content or the resin (calculated as polyvinyl acetate) is less than 5 percent and the ratio of the ketal to acetal content is not less than .5 to 1 and does not exceed 3.25 to 1, and

a plasticizer therefor comprising triethylene glycol dih'exoate.

4. As a new article or manufacture, a synthetic zene solution at 60 degrees F.) with methyl ethyl ketone and butyraldehyde and characterized by the fact that the vinyl alcohol content of the resin (calculated as polyvinyl alcohol) ranges between 10 and 28 percent, the vinyl acetate content of the resin (calculated as polyvinyl acetate) is less than 5 percent and the ratio of the ketal to. acetal content is not less than .5 to 1 and does not exceed 3.25 to 1.

JOSEPH D. RYAN. FRED B. SHAW, Js. 

